The major components of most soils are inorganic. These constituents are derived from the weathering of rocks and minerals or from subsequent reaetions and interactions of the weathering products. During the weathering and interactions of weathering products, in organic soil colloids are formed. Large amounts of inorganic colloids are essential in soils if they are to support luxurious plant growth. The colloids adsorb water and nutrient element s that might be lost from the soil &ystem and they release these as plants need them. They also adsorb and buffer the soil system against large excesses of soluble toxic substances that might otherwise exist as free moieties in soils. Soil and plant root interactions occur across two interfaces. One is the interface between plant roots and the liquid phase and the other is the interface between the soil particles and the liquid phase. Reaetions across the interface between colloid crystals and the soilliquid phase may also suppress the availability of nutrient elements to plants. The effectiveness of these interfaciaI reaetions in supporting optimum plant growth ultimately depends on the arrangements of ions in the surfaces and subsurfaces of the mineraI crystals. For this reason much of this volume is devoted to the arrangement of ions in crystalline mineraI particles commonly occuring in soils and the properties that these particles contribute to soiI systems."

Organic substances returned to the soil by plants, animals and microorganisms go through biochemical cycles and subcycles that provide essential media for the growth of plants in the soil. These cycles involve numerous, complicated and interdependent chemical reactions. Many books have been written to describe the genesis, the nature and the reactions of soil organic matter and have contributed much to organizing parts of the knowledge about soil organic matter. Each book is an important contribution but none has duplicated any of the others to any great extent; each has developed essential but loose fitting segments of the knowledge about soil organic matter. Each of these books complements the other. The authors of chapters in this volume have done considerable, scholarly research in their areas and have reported a very comprehensive coverage of their topics. Their contributions will be important supplements to already published works on soil organic matter. The editor wishes to express his appreciation for the vast library resources of the University of Illinois that were used during the production of this volume. He also wishes to express his appreciation for the help of his wife, Flossie Y. Gieseking, who assisted or promoted every operation until it was completed. Urbana, Illinois JOHN E. GIESEKING August 30, 1974 v Contributors Anderson, G., The Macaulay Institute for Soil Research, Craigiebuckler, Aberdeen, Scotland. Babel, U., Biopedologie, Universitlit Hohenheim, Stuttgart, Germany. Beute spacher, H., Institut fUr Biochemie des Bodens der Forschungsanstalt fUr Landwirt schaft, Braunschweig, Germany."